4.2.5 Compliance options

These options control what GnuPG is compliant to. Only one of these
options may be active at a time. Note that the default setting of
this is nearly always the correct one. See the INTEROPERABILITY WITH
OTHER OPENPGP PROGRAMS section below before using one of these
options.

--gnupg

Use standard GnuPG behavior. This is essentially OpenPGP behavior
(see --openpgp), but with some additional workarounds for common
compatibility problems in different versions of PGP. This is the
default option, so it is not generally needed, but it may be useful to
override a different compliance option in the gpg.conf file.

--openpgp

Reset all packet, cipher and digest options to strict OpenPGP
behavior. Use this option to reset all previous options like
--s2k-*, --cipher-algo, --digest-algo and
--compress-algo to OpenPGP compliant values. All PGP
workarounds are disabled.

--rfc4880

Reset all packet, cipher and digest options to strict RFC-4880
behavior. Note that this is currently the same thing as
--openpgp.

Try to be more RFC-1991 (PGP 2.x) compliant. This option is
deprecated will be removed in GnuPG 2.1.

--pgp2

Set up all options to be as PGP 2.x compliant as possible, and warn if
an action is taken (e.g. encrypting to a non-RSA key) that will create
a message that PGP 2.x will not be able to handle. Note that ‘PGP
2.x’ here means ‘MIT PGP 2.6.2’. There are other versions of PGP 2.x
available, but the MIT release is a good common baseline.

This option is deprecated will be removed in GnuPG 2.1. The reason
for dropping PGP-2 support is that the PGP 2 format is not anymore
considered safe (for example due to the use of the broken MD5 algorithm).
Note that the decryption of PGP-2 created messages will continue to work.

--pgp6

Set up all options to be as PGP 6 compliant as possible. This
restricts you to the ciphers IDEA (if the IDEA plugin is installed),
3DES, and CAST5, the hashes MD5, SHA1 and RIPEMD160, and the
compression algorithms none and ZIP. This also disables
–throw-keyids, and making signatures with signing subkeys as PGP 6
does not understand signatures made by signing subkeys.

This option implies --disable-mdc --escape-from-lines.

--pgp7

Set up all options to be as PGP 7 compliant as possible. This is
identical to --pgp6 except that MDCs are not disabled, and the
list of allowable ciphers is expanded to add AES128, AES192, AES256, and
TWOFISH.

--pgp8

Set up all options to be as PGP 8 compliant as possible. PGP 8 is a lot
closer to the OpenPGP standard than previous versions of PGP, so all
this does is disable --throw-keyids and set
--escape-from-lines. All algorithms are allowed except for the
SHA224, SHA384, and SHA512 digests.